linux-kernel - Re: [PATCH v6 01/16] sched/core: Allow sched

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Date:   Fri, 25 Jan 2019 13:56:46 +0000
From:   Alessio Balsini <balsini@...roid.com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-api@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Quentin Perret <quentin.perret@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v6 01/16] sched/core: Allow sched_setattr() to use the
 current policy

Hello Patrick,

What do you think about the following minor changes:

On Tue, Jan 15, 2019 at 10:14:58AM +0000, Patrick Bellasi wrote:
>  /* SCHED_ISO: reserved but not implemented yet */
>  #define SCHED_IDLE		5
>  #define SCHED_DEADLINE		6
> +/* Must be the last entry: used to sanity check attr.policy values */

I would remove this comment:
- the meaning of SCHED_POLICY_MAX is evident, and
- should we hint on how the value is used? That comment will be removed
  the next time SCHED_POLICY_MAX is used for something else.
  This is what should also happen to the comment of SETPARAM_POLICY:
  now sched_setparam() is no more the only code path accessing
  SETPARAM_POLICY.

> +#define SCHED_POLICY_MAX	7

+#define SCHED_POLICY_MAX    SCHED_DEADLINE

This would make it compliant with the definition of MAX.

> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4560,8 +4560,17 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
>  	if (retval)
>  		return retval;
>  
> -	if ((int)attr.sched_policy < 0)
> +	/*
> +	 * A valid policy is always required from userspace, unless
> +	 * SCHED_FLAG_KEEP_POLICY is set and the current policy
> +	 * is enforced for this call.
> +	 */
> +	if (attr.sched_policy >= SCHED_POLICY_MAX &&

+	if (attr.sched_policy > SCHED_POLICY_MAX &&

In line with the previous update.

> +	    !(attr.sched_flags & SCHED_FLAG_KEEP_POLICY)) {
>  		return -EINVAL;

Thanks,
Alessio